DE19920225B4 - Process for the production of reinforcing and / or process fibers based on vegetable fibers - Google Patents

Abstract

method for the production of reinforcing and / or process fibers based on vegetable fibers, characterized in that the fiber material is ground in a fluidized air mill.

Description

The The present invention relates to a process for the preparation of gain and / or process fibers based on plant fibers whose elementary fibers fibrillate are.

plant fibers For example, bast fibers include those from plant stems obtained from fiber plants. The bast fibers settle out Fibers composed of several elementary fibers, the single cells to fiber bundles united. In the fibrillation is an elementary fiber, the typically has a diameter between 10 microns and 30 microns, laterally in finer Fibers, which are called fibrils, split. The length of such Fibrils are typically smaller than 300 microns and their diameter is between 1 μm and 5 μm. In usually the fibrils remain fibrillated at one end connected to the fiber.

Of further, the plant stems of bast fiber plants have shives on. Under it understands. the woody bark fibers are not included Components of fiber plants.

Conventionally, reinforcing or processing fibers are made on the basis of synthetic aramid fibers which are fibrillated by means of special mills. In 4 a micrograph of a fibrillated aramid fiber is shown. Fibrillation gives a fiber a macroscopic woolly habit.

When process fibers fibrillated aramid fibers have beneficial effects on processing properties in composites of the chemical industry, such as in friction linings and seals. The aramid fibers are characterized thereby, that with they have a particularly high proportion of fibril during fibrillation can be achieved.

adversely however, fibrillated aramid fibers are very expensive and toxic Decomposition products, such as hydrocyanic acid, at high temperatures can release so that theirs Disposal is problematic.

Furthermore, there are reinforcing or processing fibers based on plant fibers or organic natural fibers. Such fibers are in the DE 197 03 634 A1 described. The fibers described therein can be obtained by digestion by means of ultrasound, wherein the fibers are dissolved out of the existing in the stems composite and a separation of the fibers takes place. It is known to wet wet such fibers. In this way, however, one has previously received another type of fiber, namely a very short, crushed elementary fiber. The typical structure of a fibrillated fiber having elemental fibers having an average diameter of about 15 microns and at one end with these associated fibrils having an average diameter of less than 5 microns is not obtained with such a wet grinding process. However, the Blaine-Dyckerhoff specific surface area explained below is relatively high in these wet-milled fibers. The reason for this, however, is not a high degree of fibrillation, as defined here, but the strong shortening of the fibers. So far fibers based on vegetable fibers could not replace synthetic fibrillated aramid fibers.

It is therefore the object of the present invention, a method for the production of reinforcing and / or process fibers be based on plant fibers and the synthetic can replace fibrillated aramid fibers.

A Another object of the present invention is a method for the production of plant fiber-based reinforcing and / or to provide process fibers that fibrillated well Aramid fibers mix.

at the method according to the invention for the production of reinforcing and / or process fibers based on plant fibers is the Milled fiber material in a fluidized air plant. By use Such a grinding plant could be a particularly good fibrillation the elementary fibers of the plant fibers are obtained. advantageously, can as a starting material by ultrasonically digested fiber material, which may also include shovels may be used.

at the inventively prepared gain and / or process fibers based on plant fibers whose elementary fibers fibrillate the fibril content of the elementary fibers can be greater than 3 area percent and less than 50 area percent be. With such a high proportion of fibrils, the amplification and / or process fibers replace fibrillated aramid fibers in many areas.

The fibers of the invention can in this case, for example, on flax, hemp, sisal, jute or ramie fibers based. Advantageous to the use of such plant fibers is, that you a much lower price than synthetic aramid fibers own and at high temperatures or disposal no ecological problematic products arise.

It can the fibers of the invention be mixed with fibrillated aramid fibers, so priced favorable gain and / or process fibers manufacture. In this case, the proportion by weight of the fibers according to the invention between 10% and 90%, with a weight percentage between 50% and 80% is preferred.

It can the fibers of the invention either largely free of shives or of a mixture fibrillated fibers and shives exist. It is depending on Application advantageous, either the proportion of shives below 10 wt .-% to keep or high heel content between 25 wt .-% and 75% by weight. Such a fiber-shaving mixture has the advantage that it is cheaper as a pure fiber material. Furthermore, such a mixture is at some applications, e.g. for friction linings, where additional fillers he wishes are, advantageous.

It a friction lining or a gasket can be made which is the fibers of the invention to grasp.

in the Following are exemplary embodiments of the present invention with reference to the drawings.

1 shows a microscope image of a fibrillated hemp fiber,

2 shows a microscope image of a mixture with 80 fibrillated hemp fibers and 20% fibrillated aramid fibers,

3 shows a microscope image of a mixture with 50 fibrillated hemp fibers and 50% fibrillated aramid fibers,

4 shows a micrograph of a conventional fibrillated aramid fiber.

1. First embodiment:

At the first embodiment were the fibers of the invention produced by means of a laboratory mill. As a laboratory mill was a for another purpose designed mill for the production of powders used in the food industry. The mill is made by the company Moulinex and is commercially available under type designation 320. It was surprisingly found that with such a laboratory mill a particularly good fibrillation of Pflanzenfa fibers, in particular of hemp fibers could be achieved.

The laboratory mill consists of a cylindrical stator and one in the axis of the Stator cylinder arranged rotor. There are two blades on the rotor attached, which extend radially to the stator. At a radial length the knife of about 50 mm are the two knives in the vertical direction by 12 mm against each other added. The laboratory mill is characterized in particular by the fact that on the inner wall of the stator on the ground every 10 ° inside ribs are provided, which are approximately up to the height of the upper knife on the inner wall extending parallel to the rotor axis. It is believed that the particularly good fibrillation of the hemp fibers by these inner ribs is produced, as in a comparable mill without inner ribs a very much worse fibrillation of hemp fibers was produced. It it is further assumed that in a length the starting fibers of less than 20 mm prevent the inner ribs that yourself the fiber material turns with the knife.

At the first embodiment were the fibers of the invention produced by hemp fiber material with a proportion of shives of less than 10 wt .-% in the laboratory mill given was ground there and between 30 and 90 sec. The length of the Starting hemp fibers was shorter as 20 mm.

1 shows hemp fibers fibrillated with the laboratory grinder as described above, with the meal being 90 seconds. Clearly visible are the elementary fibers, from which individual smaller fibrils branch off. As with the aramid fibers, one end of the fibrils is bonded to the respective parent elementary fiber.

The Fibers, according to the first embodiment were prepared, with the laboratory mill 90 sec on the elementary fibers has been referred to in the following as A.

2. Second embodiment:

In the second embodiment, a commercial grinding plant from Altenburger Maschinen Jäckering GmbH (Ultrarotor Model IIIa, 75 kw) was used. Such a grinding plant is in the DE 35 43370 A1 described. In this mill, the regrind particles are accelerated to a high speed within the plurality of air swirls generated by the refining plates. It is assumed that the mutual collisions of the regrind particles produce the grinding process. In particular, the grinding takes place only to a small extent by the meeting of the Mahlgutteilchen with the fixed and rotating machine parts. For this reason, the grinding system used here is referred to as vortex air grinding plant.

Surprisingly The fibrillated fibers produced with the laboratory mill could be used with this grinding plant reproduced and with modified settings of the grinding plant even be improved.

When Starting material for the production of the reinforcement according to the invention and / or process fibers may be organic Natural fibers or vegetable fibers, such as flax, hemp, Sisal, jute or ramie fibers are used. As a particularly advantageous has become the use of ultrasound hemp as Starting material proven. The proportion of shives is here in the Usually less than 10% by weight. The length of the starting material was shorter as 20 mm. Furthermore, as a starting material, a fiber-shaving mixture be used, wherein the proportion of shives between 10 wt .-% and 95 wt .-% may be.

According to the second embodiment Three different fibrillated hemp fibers were produced. The fibers were each at different negative pressure in the Milling grinding plant. For fiber B1, the negative pressure, i. the pressure difference to normal pressure, 45 mbar, with the fiber B2 25 mbar and for fiber B3 12 mbar. The negative pressure causes the fiber material conveyed through the grinding plant so that the Residence time of the fiber material in the grinding plant at higher negative pressure is shorter. Thus, the residence time was at a pressure of 12 mbar under normal pressure about 1 second and at the suppression of 25 and 45 mbar 1/2 sec and less. During the grinding process was the temperature in the grinding plant never exceeds 20 ° C.

3rd Comparative Example C:

When Comparative Example C were fibrillated fibers from Schwarzwälder Textilwerke Heinrich Kautzmann GmbH, Schenkenzell examined, using as starting material in turn, ultrasonically digested hemp fibers were used. The results of this study are shown in Table 1.

4. Comparison of the fibers according to the invention with Comparative Examples C:

Around the fibers of the invention to characterize and compare with the reference fibers were examined the fibrillated fibers microscopically. It was a Microscope of the company Carl Zeiss Jena (Binocular "Citoval 2"; Eyepiece: 16x; Lens: Zoom 0.63 to 6.3 times). To set the scale was an eyepiece micrometer. The geometric dimensions of the fibers and fibrils became semi-quantitative estimated where the accuracy (one sigma) to 25%, based on the respective Measured value, is estimated. As enlargement was in the measurement of the fiber lengths 10: 1 selected (Lens 1.0-fold) and for the measurement of the fiber diameter 50: 1 (lens 5.0-fold).

in the Following are the terms used to characterize the fibrillated Fibers are used, defined.

Fiber bundles:

When fiber bundles here are two or more at least partially contiguous elementary fibers designated. The diameter of a fiber bundle is of the order of magnitude between 0.04 mm to 0.4 mm, with 80 area percent of those considered Fibers are in this area. For diameters greater than 0.15 mm is the cross-section of the fiber bundle oval, where as the diameter the largest transverse extent is specified.

Elementary fibers:

When Elementary fibers are called single fibers, with 80 area percent The fibers considered have a diameter between 0.01 mm to 0.03 mm own. An elementary fiber biologically represents a cell.

fibrils:

When Fibrils become one end for the purpose of the comparison made here denoted associated with an elementary fiber finer fibers whose Diameter in the range between 0.002 mm and 0.01 mm and their length between 0.01 mm and 0.1 mm, again each 80 area percent the considered fibrils are in this range.

fibrillation:

By the degree of fibrillation should be estimated, which proportion the length an elementary fiber has fibrils. This is done at the microscopic Investigation of an elementary fiber divided into areas of 1 mm in length. It is then determined whether a 1 mm long area at least one Fibril or not. The Fibrillierungsgrad is then the Number of 1 mm long areas with fibrils divided by the total number of the examined areas. This results in a Fibrillierungsgrad of 100%, if in each case after 1 mm at least one fibril at the Elementary fiber occurs. If fibrils are greater than 1 mm along the elementary fiber occur, the Fibrillierungsgrad less than 100%.

Proportion of fibrils:

By The measurement of fibril content is intended to be a more accurate method for disposal be placed to detect the fibrillation of an elementary fiber. For this elementary fibers are examined microscopically. It will the area determined in the microscope image, which occupy the fibrils, and the area, which are taken by the elementary fibers. The fibril content in area percent results from the area the fibrils divided by the sum of the fibrils and the elementary fibers occupied area.

wobei a der Fibrillenanteil in Flächenprozenten ist und d das Verhältnis des Durchmessers der Elementarfaser zu dem Durchmesser einer Fibrille. Bei der Umrechnung wird als Näherung angenommen, daß die Fibrillen und die Elementarfasern die gleiche Dichte und jeweils über ihre gesamte Länge den gleichen Durchmesser aufweisen.The fibril content in area% (area%) can be converted into a proportion of fibril in wt% by the following formula:

where a is the fibril fraction in area percent and d is the ratio of the diameter of the elementary fiber to the diameter of a fibril. In the conversion, it is assumed as an approximation that the fibrils and the elementary fibers have the same density and the same diameter over their entire length.

Of Further, the indication "80 % "behind one Feature in Table 1 that 80 Area percent of consider fibers or fibrils within the specified range lie.

Specific surface after Blaine-Dyckerhoff:

Furthermore, Blaine-Dyckerhoff's specific surface area of the fibers was determined. The measurement was carried out using a Blaine air permeability method (DIN EN 196, Issue 3.90, Part 6). The Experimental procedure is as follows:
First, the density Dd of the fibers to be measured is determined. For cellulose fibers, this is usually between 1.2 and 1.5 g / cm ³ , typically 1.4 g / cm ³ . From this density and the volume Vd available in the measuring cell, the mass Md of the fiber material to be measured is given by Md = Dd · Vd · e, where e is the porosity. The porosity is defined as the quotient of the pore volume and the total volume. It has the value of 0.500 here. In the measuring cell, the fiber material is pressed cold between two round filter until the measuring cylinder can be completely closed. In the measuring method, the time is now measured, which requires a certain amount of gas (usually air) in order to flow through the fiber material in the measuring cell at a fixed, initial negative pressure. In this case, the time is detected that the liquid level in a U-tube manometer communicating with one end of the measuring cell needs to go through a fixed height difference.

wobei c ein durch Eichung bestimmter Koeffizient ist.The specific surface according to Blaine-Dyckerhoff is then calculated as follows:

where c is a coefficient determined by calibration.

The above-mentioned DIN method provides a fixed value for the porosity of 0.500. If the volume of the measuring cell is not sufficient for the fiber material used, so that the mass of the fiber material calculated from the density and the volume of the measuring cell is actually smaller, the porosity shall be calculated as follows: e = 1 - Md / (Vd · Dd)

The specific surface according to Blaine-Dyckerhoff is then given as follows:

The surface according to Blaine-Dyckerhoff is correlated with the actual specific surface, being the actual specific surface by normalizing to a comparison standard with known specific surface can be determined exactly. The specified in the table below readings however, they are not normalized but give in to the specific surface Blaine-Dyckerhoff.

at The measurements were carried out by an air permeability tester from Toni Technik, Berlin after Blaine used (type ToniPERM).

The above-mentioned calibration coefficient c in this apparatus was about 1,200 sec ^-1/2 cm ^-1 .

in the The following summarizes in Table 1 the results of the measurements.

Table 1:

It is noticed that when Starting material of fibrillation degree less than 20 percent and the fibril content of an elementary fiber is less than 1 area percent or 0.2 percent by weight. It follows that the fibers of the invention B1, B2, B3 and A are all higher Fibrillation degree and a higher fibril content an elementary fiber as the comparison fiber C. The comparison between the according to the embodiment 1 (A) and according to the embodiment 2 (B1, B2, B3) shows that in each case a similarly high Fibrillierungsgrad results, with the Fibrillierungsgrad and the fibril content in the embodiment 2 used Improve grinding system thereby that the grinding at a lower negative pressure, i. e. that the fibers are longer in dwell on the grinding plant.

If one compares the respective specific surfaces according to Blaine-Dyckerhoff of the fibrillated fibers, it is also found here that this is higher in the case of the fibers produced according to the invention than in the comparison fiber C. The fiber B3 produced according to the invention even reaches the Blaine specific surface area. Dyckerhoff of fibrillated aramid fibers approach, which is between 7000 cm ² / g and 12000 cm ² / g.

However, the specific surface area must always be considered in connection with the mean length of the elementary fibers, since a high specific surface area is also due to strongly shortened ground electrons mentarfasern can be produced. In this case, however, there is another type of fiber that may also have very small diameter fiber fragments but no small diameter fibrils attached to their larger diameter parent elementary fibers. In this respect, Blaine-Dyckerhoff's specific surface area for fibrillation is only of limited significance.

5. Mixture of the fibers according to the invention with fibrillated aramid fibers:

The fibrillated according to the invention Fibers can be used as reinforcement or process fibers use. In particular, the fibers of the invention can be advantageous in seals and friction linings and in composite materials, e.g. in the plastic and building materials sector.

Furthermore, mixed fibers can be produced particularly advantageously with the fibrillated fibers according to the invention if they are mixed with pure fibrillated aramid fibers. Such mixed fibers have a particularly high strength and an almost identical fibril structure as pure aramid fibers, so that they can be used for example in seals and friction linings. The fibrillated plant fibers may be provided in the mixture in a proportion by weight of 10% to 90%, with a proportion between 50% and 80% has proven to be particularly advantageous. In the 2 and 3 Microscope images of such mixed fibers are shown, in 2 fibrillated aramid fibers of 20% by weight and fibrillated hemp fibers of 80% by weight are contained in the mixture and in 3 shown mixture fibrillated aramid fibers and fibrillated hemp fibers are contained in equal proportions by weight. The scale is the same in all pictures. He turns out 4 ,

6. Fiber-Shaving Mixtures:

Of others can According to the invention fiber-shaving mixtures be fibrillated. Such mixtures are cheaper as the use of pure fibers as starting material and are at special applications where additional fillers are desired, advantageous.

Under Shoveling is understood to mean the non bast fibers contained, woody Components of fiber plants.

The Fiber-shaving mixture is used as starting material for the fibrillation, as described in the first and second embodiments is used. After execution receives the fibrillation Fibrillated elementary fibers of plants or organic natural fibers on the one hand and ground shives on the other. To a large extent jack-free gain or process fibers To obtain the Schebenanteil of the starting product under 10 % By weight, advantageously less than 2% by weight. Is a higher proportion of shives, for example, as an additional filler desired this is typically between 25 wt .-% and 75 wt .-% (whole plant). In general, the proportion of scrap can be between 0% by weight and 95% by weight. lie.

7. friction linings

In addition to the fibers according to the invention, friction linings generally comprise organic and / or inorganic fillers, lubricants, organic binders and / or metals or metal compounds. In general, the friction linings contain about 0 to 70 wt .-%, in particular 1 to 70 wt .-%, metals, about 3 to 50 wt .-% fillers, about 10 to 45 wt .-% lubricants and about 3 to 25 wt .-% fibers. As lubricants graphite, molybdenum disulfide, antimony trisulfide, lead sulfide or tin sulfides (SnS, SnS ₂ ) are useful. When tin sulfides are used as lubricants, they are generally contained in an amount of 0.5 to 10% by weight, preferably 2 to 8% by weight, based on the total amount of the lubricants.

Claims (3)

Process for the production of reinforcing and / or process fibers based on vegetable fibers, characterized in that the fiber material is ground in a fluidized air mill. Method according to claim 1, characterized in that that this Fiber material was digested by ultrasound before grinding. Method according to claim 1 or 2, characterized that as Starting material is a fiber-shaving mixture is used.